virt-aa-helper: apparmor wildcards to forbidden chars
    
    Some globbing chars in the domain name could be used to break out of
    apparmor rules, so lets forbid these when in virt-aa-helper.
    
    Also adding a test to ensure all those cases were detected as bad char.
    
    Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>